The present invention relates to a communication control method and a network system that are used for avoiding traffic congestions at a network node or the like.
In a network environment where the broadband communication has been becoming predominant, a variety of applications have emerged on the market. These applications have different qualities of required service depending on the purposes of the applications.
The applications include the one continuously required a high communication quality as is the case with an audio or moving-picture application. The number of such demands is expected to increase in the future where apparatuses at a home are connected to each other by a network for seamless communication with the Internet.
Technologies for assuring these communication qualities are collectively referred to as a Quality of Service (hereinafter referred to as “QoS”) technology. As a QoS technology, there have been proposed a variety of techniques known in the prior art. Representatives of the QoS technologies include polishing/shaping, flow control, priority control and signaling.
Polishing is a technology by which a processing load applied by an apparatus receiving packets is reduced by discarding packets received after a prescribed number of receivable packets is exceeded.
Shaping is a technology often adopted in conjunction with the polishing technology. In the shaping technology, when apparatus transmits packets, packets to be processed are not transmitted instantly but are transmitted with consideration of time balance of the traffic. The concept of the shaping technology is shown in FIG. 10.
By adoption of the shaping technology, load balance in the media is smoothed, making it possible to avoid a situation in which much traffic occurred instantaneously.
In addition, the polishing/shaping technologies are capable of raising the resource-supplying efficiency of links for other communication apparatus existing in the network without requiring special implementations.
The flow-control is a technology for avoiding a congestion state of the network by transmission of a congestion signal to a traffic source to suppress the output of the traffic source when much traffic cause an overflow of an input buffer in an apparatus serving as a traffic destination as shown in FIG. 11.
By adoption of this technology, a packet can be prevented from being discarded by the polishing technology adopted on the reception side in a state of congestion. This technology is known as a back pressure in the half-duplex system. In a full-duplex system, on the other hand, this flow-control technology is defined by IEEE-802.3X specifications as a technique for transmitting a pause frame.
In addition, the flow-control technology is effective in that discard of packets by polishing technology can be avoided priorly.
The priority-control is a technology for transmitting certain traffic of packets in precedence of other traffic of packets after making priority comparison between them as shown in FIG. 12.
By adoption of the priority-control technology, data such as audio and moving-picture data can be transmitted at a high quality without turbulences. This technology is defined by IEEE-802.1p and DiffServ (RFC 2474) specifications. In addition, this technology is also generally referred to as a CoS (Class of Service) technology.
The priority-control technology is capable of providing a high-quality service by execution of control to give a high priority level to a specific piece of traffic in a range not exceeding the speed of the link.
The signaling technology is a technology for reserving a resource such as a band in advance for a route of traffic and not transmitting a packet prior to a stage at which the reservation is accepted as shown in FIG. 13. Since resources provided specially for the traffic are allocated for the transmission, the reliability of the transmission is very high. As long as a packet is transmitted in the range of reserved resources, there will be no state of traffic congestion and no packet will be discarded.
In addition, a request for a reservation of a resource for a traffic that seems to exceed the speed of the link is rejected. Thus, in traffic with a resource once reserved, the quality does not deteriorate due to disturbance.
In addition, since protection against worst delay is assured, this technology is suitable for real-time audio and moving-picture communications. Signaling protocols include RSVP (RFC 2205) and SBM (RFC 2814). In general, the QoS technology refers to this signaling technology.
However, the QoS technologies described above have the following problems.
First of all, in the case of the polishing technology, when polishing occurs, a discarded packet cannot be transmitted normally. For this reason, polishing should not be adopted in ideal communications.
In addition, in the case of the polishing/shaping technologies, all pieces of traffic are implemented in the best-effort type transmission. Thus, there is no means for avoiding a missing packet in the event of a traffic congestion.
Furthermore, in the case of the flow-control technology, it is necessary to implement the same flow-control mechanism on both the transmission and reception sides. Moreover, a uniform congestion control signal independent of the traffic type is transmitted so that best-effort data and stream data such as sounds and moving pictures are treated in the same way as an object of suppression. As a result, there is virtually no mechanism for protecting a piece of traffic with higher priority.
In addition, in the case of the priority-control technology, there is no means for discriminating and protecting a high-priority piece of traffic exceeding the speed of the link. Thus, such a high-priority piece of traffic brings about an adverse effect to all other high-priority pieces of traffic including a piece of traffic carried out normally. Furthermore, since there is no mechanism for suppressing a burst of traffic, a packet is possibly missed in a state of congestion.
Moreover, while the signaling technology has highest reliability among the QoS related technologies, this technology is not suitable for an environment in which a number of short traffic are generated. This is because a resource on a route of a traffic flow must be reserved.
In addition, since it is necessary to implement a uniform signaling protocol for all apparatus on the traffic route in order to assure the traffic completely, this technology has a lack of versatility. In the present state of the art, it is hard to say that the signaling protocol has become popular in a wide range of fields. Thus, there is raised a problem as to how to make the protocols uniform and how to implement the uniform protocol in a variety of apparatus.